عنوان مقاله [English]
Introduction: the capacity to sense and respond to light is widespread in animals, plants, fungi and bacteria. In nature, light is one of most crucial environmental signals for developmental and physiological processes in various organisms, including filamentous fungi. The ability to sense light is crucial for many organisms determining timing and modality of development and orienting primary and secondary metabolic processes. Due to the increased number of sequenced fungal genomes, numerous genes encoding proteins involved in light sensing and downstream gene regulation have been identified. This expedited understanding the mechanisms by which the fungus activates physiological and morphological reactions in response to light. One of the One of these fungi is the Monascus purpureus. the genus Monascus was classified in the family Monascaceae, but based on recent genome sequencing, it seems that the genus is more closely associated with the genus Aspergillus, and thus should be reclassified in the Aspergillaceae family. The fungus Monascus is the most famous for production of pigments and monacolins; however, it can also form other metabolites – citrinin, dimerumic acid, and GABA (γ-aminobutyric acid). Formation of particular metabolites depends on the strain and cultivation conditions. Monascus pigments (MPs) as natural food colorants have been widely utilized in food industries in the world, especially in China and Japan. Moreover, MPs possess a range of biological activities, such as anti-mutagenic and anticancer properties, antimicrobial activities, potential anti-obesity activities, and so on. So, in the past two decades, more and more attention has been paid to MPs. In this study, the effect of different LED light spectra on growth and secondary metabolites of Monascus purpureus is studied.
Material and methods: In this study, in order to investigate the effect of light quality on growth rate, biomass and pigment production in Monascus purpureus, this fungus was cultivated under dark conditions and three light, white, red and blue LEDs and harvested in three times (seventh, tenth and fourteenth days) To measure the amount of pigment in the liquid medium. To measure the radial growth rate and biomass weight, a solid medium was used. Also, the absorbance of the samples was measured in 410, 470, and 510 nm wavelengths for yellow, orange and red pigments,respectively, using a spectrophotometric device.
Results: The results of this study shows that there is a significant correlation between pigment and optical spectra, so that the highest amount of pigment (yellow, orange, red) was obtained in terms of darkness, with values of 0.344, 0.291, 0.249, respectively. There was no significant difference between harvest time and pigment content except for red color on day 10 in dark conditions, with a value of 0.249. The smallest amount of pigment is also related to the red pigment produced on the 14th day in the blue light spectrum with an absorption of 0.009. Also, the highest radial growth rate was observed in the dark condition with a mean growth of 5.12 mm / day and the lowest radial growth was related to the cultivation of monascus under the blue light spectrum with an average growth of 2.61 mm / day. However, there was no significant difference between biomass and light in solid media. The highest amount of biomass in the liquid medium was 0.126 g in 40 ml of culture medium with monascus culture in dark conditions on day 14 and the lowest amount of biomass was also obtained with 0.068 g in 40 ml of culture medium in white light on the seventh day.
Concolusion: The results showed that, in addition to factors such as carbon source, nitrogen source, PH, temperature, minerals, partial pressure of oxygen, other microorganisms, light is also an important environmental factor for development and physiological processes in Monascus purpureus. According to this study, the growth of this fungus in the dark causes increased cell growth, the amount of biomass and pigment, these results indicate that the lack of light stimulates the growth and production of secondary metabolites in this fungus. Although there was no significant difference between pigment value and harvest time, except for the red pigment, but due to the slight difference in pigmentation on the 10th day of cultivation in dark conditions, it can be deduced that the best conditions for producing the highest amount of pigment, cultivation of Monascus fungus under conditions The darkness and harvest of this mushroom is on the tenth day of cultivation. Also, among pigments produced by this fungus, the amount of yellow pigment production in different light conditions is higher than other pigments. Chen, M. H. & Johns, M. R. (1993) shows that the solid-state yielded greater amount of pigment9,8 compared to submerged fermentation. This phenomenon had been attributed to the pigment because of low solubility in the fermentation medium and pigment accumulation within the mycelium in submerged culture10. In contrast, in solid-state fermentation, the Monascus sp penetrated into solid substrate and pigment released onto the surface. Solid state not only issued nutrient, but also acted as anchorage for cells, this may have bestowed to the celebrated eminent productivity. Solid state environment is similar to environment of fungi which was normally excited. Therefore, it is suggested that in subsequent studies, to achieve maximum pigment, a solid culture medium should be used.